HVAC Control in the New Millennium.pdf - HVAC.Amickracing

HVAC Control in the New MillenniumSome companies like Teligent and Winstar offer transmission usingwireless radio frequencies instead of congested copper lines. Voice ordata would be transmitted from a small dish antenna on the roof to acentral office, which would then transmit the information to your ISP.Designed primarily for urban areas, this arrangement could be a lotcheaper than conventional cables.The Future of ISPAs end users and businesses move up to faster connections, thebottleneck may shift to the ISPs. The problem is one of capacity. Iflarge numbers of users with access to 1 mbps. DSL signs up for theservice, the infrastructure would probably be able to handle it. But,this is not true for 7-mbps DSL and 20- to 25-mpbs DSL will be availablein the near future. The network will not be able to handle thistraffic.In addition to selling access to end users and businesses, largenational ISPs such as Sprint, MCI WorldCom, and AT&T sell bandwidthto smaller ISPs. Those smaller ISPs connect at Network AccessPoints (or NAPs), which in turn connect them to the backbones (SeeFigure 9-2).Few businesses have cable since the cable companies did notwire business and industrial areas. But, they do have access to highspeeddedicated lines ranging from 56-kbps frame relay to 1.5-mbpsT1 lines and beyond.The Internet backbone is really several backbones today. The bignational ISPs, along with several smaller firms, own high-speed fiberopticnetworks that connect major metropolitan areas at speeds up to38 gbps. In a few years, those connections could be as fast at 200gbps.Besides T1 or frame relay lines, other technologies include theIntegrated Services Digital Network or satellite-dish access that canprovide even faster access.For many, the future lies in cable modems and Digital SubscriberLines. Both cable and DSL are much faster than analog modems.Each provides a reliable connection and fast connect times.At the end of 1998, the number of cable modems in use inNorth America was about 513,000 and the number of DSL lines in the©2001 by The Fairmont Press, Inc. All rights reserved.